The present invention relates to industrial-mechanical devices that assists in the production of semiconductors and improve the safety and efficiency of the semiconductor manufacturing environment.
Currently, there are a variety of tools available to assist the semiconductor processing personnel in handling of semiconductor wafer boats. However, much of the risk in the semiconductor-manufacturing environment still includes poor ergonomic practices, which subject the handlers to personal risk and the very expensive product to contamination risks. One of the most inefficient and risk prone dangerous areas are the horizontal furnaces used to process the silicon wafers.
There are small tools for safe handling and transporting of silicon wafers, which include vacuum wands, manual wands (wafer tweezers), vacuum pumps (spurious), tubing, and tweezers for various size wafer handling, etc. Mactronix, Amtech, TEL Tokyo Electron Ltd, Fluoro Mechanic of Tokyo, Japan, and Tystar of Torrance, Calif. are examples of companies that manufacturer these advanced wafer handling tools for the semiconductor industry.
However, currently there is very little automation of the horizontal furnace process in use despite the fact that there have been great advances in the automation of wafer handling up to and around the furnaces. The actual critical steps of loading and unloading wafers boats from horizontal furnaces despite two decade""s worth of attempts to improve productivity around the loading and unloading of furnaces, still resist the applications of automation.
This lack of automation tools around the horizontal quad stack furnace is surprising, since operators in the fabrication areas are challenged to perform awkward, inefficient, and hazardous manual tasks when in physical possession of expensive wafer loads.
Examples of overall automated material processing systems for the semiconductor manufacturing environment are contained within U.S. Pat. Nos. 6,157,886 and 6,045,235, and 5,838,566 developed by Conboy, et. al. and owned by Advanced Micro Systems of Sunnyvale, Calif. It is unclear whether such systems are commercially viable on a mass scale because of the expense of retooling of the fabrication area to employ such a customized comprehensive fabrication system. Additionally, these computer-controlled comprehensive method(s) for managing material fabrication are not really relevant to the actual physical processes involved in the fabrication area, but more to a general method of manufacturing control and optimization. Another example of complex automated material handling units is taught by U.S. Pat. No. 4,829,445, which is illustrated by FIG. 2 and invented by Burney and owned by National Semiconductor Corporation of Santa Clara, Calif. However, this invention is directed at a particular device/system for material processing but like the above patent, requires extensive installation and computer controls and expense.
In general, the complex automated solutions are too expensive. They are slow (reducing throughput), with an ever-present risk of cross-contamination, difficult to install and maintain, with a maneuverable space requirement, which is much greater in practice than claimed by some suppliers. Such systems require high cost in time, space, and expense, in most instances actually reduce the throughput of the furnace, hampering productivity. Claims made by entities investing in full furnace automation on the grounds that it prevents xe2x80x9cmiss processingxe2x80x9d by the operator are often largely exaggerated. Hence, the semiconductor industry has found it more effective to continue to employ operators despite the continued risks to both operator and product.
FIG. 1 represents a typical quad stack horizontal furnace 10 for processing semiconductor wafers. The furnace consists of four furnace tubes, with cantilevered loaders 12, 14, 16, 18 on which wafer boats containing typically 50 wafers must be carefully placed. Furnace 12 and 14 will exist at a height of 80 and 60 inches or greater respectively above the floor level. When cantilever-loading systems became popular in the 1980""s it was expected that automation of the loading and unloading of such semiconductor processing devices would quickly follow. Despite some very ambitious attempts by furnace manufacturers and other companies to automate the process, the numbers of fabricating environments employing automated furnace loading are a tiny minority. Horizontal furnace automation has been unsuccessful for several reasons, mainly capital expenditure, high maintenance costs, reduced throughput, and difficulty of installation among others.
Because automation attempts have failed due to the above-mentioned expense and convenience issues, the semiconductor wafer boats are still handled manually around the furnace. The first difficult set of actions performed by a typical operator is the action of unloading the top tube of the quad stack horizontal furnace at level 12, which is typically approximately 80xe2x80x3 above floor level. Typically, operators climb up and down (backwards) a set of 2 or 3 steps with some hand held fork lift device to remove a single wafer boat from the cantilever. The loading process is the reverse, climb up with load in one hand, load and climb down empty handed, backwards. In all a total of 24 trips are needed to load and unload (6xc3x972=12 boats=600 wafers) the wafer boats from a typical single tube process.
What is needed is a simple solution to bridge the gap between the expense and complexity of full automation and reducing the responsibility and risks to operators that is affordable and does not require extensive retooling of the fabrication area.
The present invention addresses many of the above discussed needs by facilitating sensible, safer and ergonomically efficient loading, unloading, and transporting of silicon wafers in the manufacturing environment, all at a relatively small cost to the semiconductor manufacturer. The present invention represents an effective low cost contribution to the improved productivity of horizontal furnace processing.
It is the object of the present invention, the Elevator/Transporter (also referred to as the xe2x80x9cE/Txe2x80x9d(trademark)), to uniquely combine a means by which batches of semiconductor wafers, can be transported back and forth between any of the furnaces (left hand or right hand configuration) and any of the xe2x80x9ctransfer stationsxe2x80x9d in the fabrication area, elevated to any required cantilever level and back down to the correct height for easy loading/unloading at the transfer station, store and queue the wafers in one self contained apparatus. The present invention is simple, affordable, requires the use of little space in the semiconductor fabrication area, and that which it does require, since it is mobile, is a non issue as it can be simply rolled out of the way as necessary to provide space.
Using the present invention, wafers are staged by the operator from the transfer station prior to hot processing and loaded into a rotating drum feature on the invention. The device is wheeled or rotated about its axis, depending on the configuration of the fabrication area, over to the furnace where the operator presses the button to raise the drum to the required, pre-set, load level. In a typical operation, using the optional steps, the operator climbs to tube level, with both hands free for safety. The operator is now able to unload the cantilever of the processed wafers and place them into the invention.
The operator rotates the drum bringing up the next batch for the furnace and while still in position loads the cantilever and starts the next run. The operator can then climb down the steps with both hands now free and wheel the invention with processed wafers safely enclosed, to the next workstation.
The resulting benefits of using the present invention are described in the bullet points below but briefly stated the present invention provides safer, quicker, more reliable furnace loading of semiconductor wafer boats, with a very low cost of ownership and a minimum of disruption to the fabrication area. This simple, cost effective solution offers some huge advantages. Although the present invention is not fully automated, it reduces both the ergonomic stress on the operator and the risk to wafers and thus improves productivity. Optional features of the invention, like automatic height elevation, also allow for the reduction of operator error.
The key features of the preferred embodiment of the invention and benefits of the invention over the existing prior art are:
The invention replaces the manual loading of 300 wafers in 6 boats and unloading of 300 in 6 boats (total 12 boats or 600 wafers moved) requiring a total of 24 trips (12 trips up and 12 trips down). The invention can be safely pre-loaded with 6 boats, from the transfer station at floor level, in the delivery drum, wheeled to the furnace and by the elevation to cantilever level and rotation of the drum, provides the operator positions in which to place 6 boats of wafers already processed in the furnace. This means that while on the steps, at the requisite cantilever level the operator can unload 6 boats, rotate the drum and load 6 boats in only 2 trips (one trip up and down) the steps instead of 24 trips. Such a reduction in trips and having both hands free drastically reduces the odds of injury to the handler and damage to the expensive product.
In a preferred embodiment, the invention will allow for the transport of 600 wafers in 12 wafer boats.
The handler usually has only one hand free while loading and unloading the expensive wafers. The present invention allows the handler to have both hands available after the wafer boats are loaded for climbing and lowering to other levels.
The present invention also allows the handler to reduce the extreme ranges of motion required to load and unload wafer boats into and out of quad stack furnace.
The present invention requires that the process tube remain open for less time than in a manual-loading situation, which means that there is significantly less chance of product cross-contamination. Throughput is also increased.
The present invention allows for the queuing of wafer boats and color-coding of the cradles into which the wafer boats are loaded for lot identification, thereby reducing the ever-present risk of miss processing. With the present invention the next batch of wafers to be processed is always ready, increasing throughput.
The present invention, unlike some complex automated systems discussed above, does not require the fabrication area to be retooled. The E/T(trademark) can be implemented in the fabrication process immediately with the exception of the xe2x80x9cshoexe2x80x9d installation, which stabilizes the E/T(trademark) at the loading station.
The footprint of the present invention is small, approximately 30xe2x80x3xc3x9730xe2x80x3 and mobile. Thus, it can be multiplexed to serve numerous furnace stacks/transfer stations in a small amount of highly valuable space. Additionally, the invention""s mobility means that it is never in the way when the furnace equipment needs servicing, which is a major disadvantage of fixed, hard automation.
In one of the preferred embodiments in which the height of the cantilevers is programmed into the elevator controls to assist the operator/handler, the programming can literally be done in a couple of minutes using the xe2x80x9cset loading/unloading heightxe2x80x9d feature.
The invention requires very little maintenance because of its simple design. The breakdown on an E/T(trademark) while unlikely will only require minutes to repair, whereas automated systems could take days or weeks to repair, at multiples of costs of the purchase of a single E/T(trademark).
The invention has an optional feature where the boat trays are color coded for Lot Tracking.
The ET has xe2x80x9con boardxe2x80x9d storage of the Lift Tools so that they are always available at the point of use, which further facilitates safety and ergonomic efficiency.
The invention saves money over full automation. If full automation is used instead of present invention then one system per furnace stack is required, each costing up to ten (or greater times the price of the invention.
The invention is designed so that there is no wafer over wafer movement, which reduces the risk of wafer damage and particle contamination.
The invention includes means for loading silicon wafer boats into a series of circularly placed storage half cylindrical trays (herein also referred to a xe2x80x9ccylindrical cradlesxe2x80x9d or xe2x80x9ccradlesxe2x80x9d), which are contained, on a rotating drum. The drum not only allows for easy loading of a silicon wafer boat, onto a cantilever and into the furnace, but can be raised and lowered to a pre-determined height pneumatically, hydraulically or electrically, to allow for easy load for any furnace height.
In addition to the improved ergonomics of wafer boat loading and unloading, the rotating drum allows for multiple cradles, which are designed for xe2x80x9coffsetxe2x80x9d boat positioning and the correct queuing of the wafer boats. This provides the operator with a positive visual guide to the sequenced loading/unloading of the boats meaning that they are less likely to misprocess the product by placing the wafer boats in the wrong location.
An optional embodiment of the invention includes an attachment for steps, which may or may not include the option to have steps or an elevating platform (with or without a safety gate) built into the elevator-transporter body. A preferred embodiment of the invention leaves the step features out so that each fabrication area using the E/T(trademark) can use stairs that comply with local, state, and federal regulatory standards regarding the use of stairs or elevating platforms.
The invention also includes an optional feature for automating the wafer transfer process between furnaces with the use of the Elevator/transporter, with the use of a automatic drum rotation. However, the preferred embodiment features the low cost elevator transporter without such automatic wafer transfer/rotator. Such an automated feature significantly drives up the costs of the invention. It is anticipated that although some semiconductor manufacturers may desire the inclusion of the mentioned optional features, low manufacturing cost will remain a primary selling point of the invention.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.